Method for manufacturing a micropump and micropump

ABSTRACT

A method for manufacturing a micropump, which may be for the metered delivery of insulin, multiple layers being situated on the front side of a first carrier layer, which has a front side and a rear side, and microfluidic functional elements being formed by structuring at least one of the layers. It is provided that the structuring of the at least one layer for manufacturing all microfluidic functional elements is exclusively performed by front side structuring. Furthermore, a micropump is disclosed.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a micropump.

BACKGROUND INFORMATION

There are micropumps for the controlled and high-precision dispensing ofinsulin. It is believed that previous micropumps have been plagued,however, by complex manufacturing processes having many nonstandardprocess steps. The many special process steps according to the previousrelated art make micropumps of this type costly and lower themanufacturing yields.

In addition, other micropumps are believed to be insufficiently accuratewith respect to the dispensed drug quantities. Micropumps for insulindispensing must operate very accurately with high metering accuracy,however, and without complex sensors for detecting dispensed insulinquantities. Active flow measurement is very problematic in connectionwith insulin, because the material reacts adversely to elevatedtemperatures, for example, in connection with so-called hot film sensorsfor flow measurement.

In addition, the lack of reliability is a serious disadvantage of knownmicropumps: thus, for example, in micropumps according to the relatedart, the dispensed insulin quantity is a function of the initialpressure in the insulin supply container, which may be placed underpressure mechanically if it is designed as a flexible bag. For example,placing or laying the pump carrier on the insulin micropump may causethe supply container to unintentionally dispense insulin, or may resultin an unintentional increase in the dose just dispensed. In view of thehazardousness of an insulin overdose, this is to be avoided under allcircumstances.

A method for manufacturing a micropump is discussed in EP 1 651 867 B1.The manufacturing of the known micropump is extraordinarily complex,because during the production process, in which different silicon layersare structured from two opposing sides, fragile intermediate statesarise again and again, for example, as shown in FIGS. 3 b and 3 c of thepublication, which must be supported in a complex fashion in order toavoid permanent damage to the micropump already during itsmanufacturing.

SUMMARY OF THE INVENTION

The exemplary embodiments and/or exemplary methods of the presentinvention are based on the object of proposing a method for the massproduction of a micropump, in which fragile intermediate states areavoided. In addition, the object includes proposing a micropump whichmay be mass produced.

This object may be achieved with respect to the method described hereinand with respect to the micropump described herein. Advantageousrefinements of the exemplary embodiments and/or exemplary methods of thepresent invention are specified herein. All combinations of at least twofeatures disclosed in the description, the claims, and/or the figuresare also within the scope of the exemplary embodiments and/or exemplarymethods of the present invention. To avoid repetitions, featuresdisclosed with respect to the method are also to be considered asdisclosed and able to be claimed with respect to the device. Featuresdisclosed with respect to the device are also to be considered asdisclosed and able to be claimed with respect to the method.

The exemplary embodiments and/or exemplary methods of the presentinvention are based on the idea of not manufacturing all microfluidicfunctional elements of the micropump, namely at least one intake valve,at least one pump chamber, and at least one outlet valve as in therelated art, by structuring multiple layers from two sides, but ratherproducing all functional elements of the micropump exclusively by frontside structuring, i.e., by structuring, in particular by etching, fromonly one direction, namely originating from a front side of a firstcarrier layer toward it. In other words, for manufacturing themicropump, it is proposed that at least one integral carrier, namely afirst carrier layer, be provided, on whose front side multiple layersare applied, of which at least one layer is structured to manufacturethe functional elements, and not from the rear side of the first carrierlayer, which may be used as the support, but rather from the front sideof the first carrier layer toward the first carrier layer. The firstcarrier layer may remain unstructured during the manufacturing of thefunctional elements and thus ensures absolute hermeticity between thefront side of the first carrier layer and the rear side of the carrierlayer, using which the carrier layer always rests on a so-called chuckof a processing station or facility during the manufacturing of themicropump. Because the carrier layer is present, which may be unharmed,during the production of the functional elements, fragile intermediatestates are advantageously avoided during the manufacturing of themicropump, whereby support films, etc., may be dispensed with during themanufacturing and thus the requirements for mass production of themicropump are provided.

In a specific embodiment of the present invention, which may be afterthe manufacturing of the microfluidic functional elements by structuringof at least one layer, a second carrier layer may be provided inaddition to the first carrier layer. This may particularly be aborosilicate glass wafer in this case, which is situated at a distanceto the first carrier layer on the front side of the first carrier layer,whereby the at least partially structured layers, which are situated onthe front side of the first carrier layer, are sandwiched between thefirst and the second carrier layers. The second carrier layer may befixed by anodic bonding, in particular on the surface of what may be thestructured layer which is furthest away from the first carrier layer. Aspecific embodiment may be provided in which the liquid is supplied tothe intake valve and/or the liquid is removed from the outlet valve, inparticular perpendicularly, through the second carrier layer, at leastone fluid channel, which may be two fluid channels, being provided forthis purpose in the second carrier layer. It is possible to introducethe fluid channels into the second carrier layer after it has beenfixed. However, in a specific embodiment the at least one fluid channelmay already be introduced into the second carrier layer before it isfixed, for example, by etching, or by laser bombardment, or by drilling,for example, using a diamond drill, or by ultrasonic drilling. Thesecond carrier layer may particularly be situated in such a manner thatit cooperates directly with an intake valve and/or an outlet valve ofthe micropump and/or directly delimits the at least one, which may bethe exclusively one, pump chamber, in particular on the sidediametrically opposite to the pump diaphragm.

By providing a second carrier layer, i.e., a second integral carrier ora second integral support layer, it is possible to remove the firstcarrier layer (after applying the second carrier layer) and thus toimplement minimal dimensions of the micropump and simultaneously, byappropriately placing the intake valve and/or the pump chamber and/orthe outlet valve, to provide space for installing actuators for themicropump, which are designed as piezoactuators in particular. The firstcarrier layer may be removed, for example, by isotropic etching, e.g.,plasma etching, and/or back grinding and/or by wet etching. After theremoval of the first carrier layer, an etch stop layer, which may alsobe indirectly situated on the front side of the first carrier layer andis to be explained hereafter, may also be removed, so that any actuatorsmay act directly on the layer provided on the front side of the etchstop layer to control the pumping action. Reference is made to thedescription of the figures with respect to a procedure for removing thefirst carrier layer.

A specific embodiment of the manufacturing procedure in which the firstcarrier layer remains unstructured during the front side structuring ofat least one layer situated in front of the first carrier layer, i.e.,on its front side, i.e., at least during the manufacturing of allmicrofluidic functional elements, may particularly be used. This ispossible in particular, because the layers are structured exclusively onthe front side of the first carrier layer.

A specific embodiment of the manufacturing procedure in which the firstcarrier layer is a layer containing silicon, in particular a siliconlayer, may particularly be used. It is conceivable to use a siliconwafer as the first carrier layer.

If a silicon wafer is used as the first carrier layer, a lower stoplayer which may contain silicon oxide is applied directly to the siliconwafer. It may be a thermal oxide. At least one contact hole may beprovided at a suitable position in order to allow electrical contactingoriginating from the first carrier layer to subsequently appliedsilicon. This electrical contact is advantageous for a later,above-mentioned anodic bonding of a second carrier layer, a current flowbeing required to form a high-strength bond to the second carrier layer,which may be configured as a glass substrate. If the stop layer isprovided directly on the first carrier layer having at least one contacthole, it may be ensured that a stop layer section is located above theat least one contact hole, so that the etching action is reliablystopped in an area above the at least one contact hole if the firstcarrier layer is later to be removed by etching after the manufacturingof the functional elements, i.e., the etching procedure always meets astop layer: either a “lower” stop layer to be explained hereafter or an“upper” stop layer (sacrificial layer) to be explained hereafter.

In a refinement of the exemplary embodiments and/or exemplary methods ofthe present invention, a base layer, which may contain silicon or ismade of silicon, may be situated on the described stop layer, which issituated directly on the first carrier layer. According to a specificembodiment, this base layer forms the foundation or base layer of thefinished micropump, to which actuators, which are explained hereafter,are applied directly. Functional element structures need not be providedin this base layer.

If a silicon wafer is not used as the starting material for the firstcarrier layer for manufacturing the micropump, it is alternativelypossible to use a silicon-on-insulator wafer (SOI wafer), the firstcarrier layer being an integral component of the SOI wafer and formingthe rear side of the SOI wafer. In a starting layer of this type, theapplication of the described stop layer and the described base layer maybe dispensed with, because these are already integral components of theSOI wafer structure. In order to be able to apply the required voltageif bonding of the second layer by anodic bonding is intended, it isnecessary to provide a suitable contact arrangement, in order, forexample, to allow the current to be supplied directly to the front SOIwafer layer (in particular the base layer) via the wafer edge, forexample, by clamps or spring contacts. This is necessary because in anSOI wafer, a contact hole is typically not provided in the stop layer itcontains.

The base layer may be formed as epitaxially manufactured polycrystallinesilicon (epi-polysilicon layer), the thickness may be in the range ofapproximately 11 μm. The base layer may optionally also be planarized,i.e., polished, for example, by so-called CMP (chemical-mechanicalpolishing).

Independently of the selected starting layer (silicon wafer or SOIwafer), in a refinement of the invention, an (upper) stop layer, whichis used as the sacrificial layer, is deposited on the base layer andstructured in such a manner that a thick stop layer (sacrificial layer)remains on selected surfaces. The stop layer may contain silicon oxideor is made thereof. Instead of the structuring of the stop layer afterits application, it is also conceivable to only apply the stop layer inspecific surface areas in a targeted manner. Surface areas in which thestop layer remains, in particular after appropriate structuring, willstop an etching process, in particular a silicon plasma etching process,during later manufacturing steps. The stop layer (sacrificial layer) maybe selectively removed thereafter (therefore the designation“sacrificial layer”), for example, to produce freestanding, mobilefunctional element structures. As noted, the stop layer may be made ofoxide and may be between approximately 4 μm and 5 μm thick, for example.In the manufacturing variant “SOI wafer,” for example, a thermal oxidemay be grown up to a thickness of approximately 2.5 μm and an oxidewhich is approximately 1.8 μm thick may also be deposited thereon, forexample, in the form of TEOS or plasma oxide, which results in a totaloxide thickness of 4.3 μm. In the manufacturing variant “silicon wafer,”thermal oxidation may be dispensed with, because intolerable stressgradients would be introduced thereby into the base layer (which may beepi-polysilicon), which would make the further use as a mechanical layermaterial impossible. For the case “silicon wafer,” the full oxidethickness may be deposited as TEOS or plasma oxide.

In a refinement of the exemplary embodiments and/or exemplary methods ofthe present invention, it is advantageously provided that a functionallayer is situated on the stop layer, which is situated, which may bedirectly, in areas on the front side of the base layer, and in the areasof the base layer not encompassed by the stop layer. The functionallayer may be an epi-polysilicon layer for this purpose, which may have athickness between approximately 15 μm and 24 μm. In particular if anodicbonding (second carrier layer) must be performed later on the surface ofthe functional layer, a planarization of the surface, for example by aCMP method, particularly may be used, independently of whether the baselayer was already planarized (either applied to a stop layer or acomponent of an SOI wafer structure). The planarization layer must levelout the topography of the surface of the functional layer andmicroscopically “smoothe” the areas for bonding.

In a refinement of the exemplary embodiments and/or exemplary methods ofthe present invention, it is advantageously provided that at least onedepression is introduced into the front side of the optional layer,which may have a depth between approximately 2 μm and 5 μm, in order toavoid contact with the second carrier layer to be bonded in this area,in particular because at least one mobile functional element may beconnected to at least one depressed area.

A specific embodiment is particularly advantageous in which at least oneanti-bond layer is applied as a valve sealing surface on the front sideof the functional layer, which may be in at least one area enclosed byat least one depression. The anti-bond layer must be composed in such away that it does not adhere to the second carrier layer during an anodicbonding action, during which the second carrier is fixed on thefunctional layer. For example, the anti-bond layer may be implemented inthe form of silicon nitride or silicon carbide or graphite, etc.Additionally or alternatively to providing at least one anti-bond layeron the front side of the functional layer, it is possible to provide atleast one anti-bond layer on the second carrier layer, in particular inthe area of the intake valve and/or the outlet valve, which reliablyprevents adhesion of the second carrier layer to the functional layereven during an anodic bonding process.

The functional layer may be structured, for example, by trench etching,in such a manner that an intake valve structure and/or a pump structureand/or an outlet valve structure are at least partially produced in thefunctional layer, i.e., functional elements of the micropump are atleast partially provided.

A specific embodiment of the manufacturing method in which the producedintake valve structure and/or the outlet valve structure include atleast one coiled spring section may particularly be used. The at leastone coiled spring may carry the valve plunger of the particular valve.Multiple, for example, two to five, coiled springs of this type, whichmay be three coiled springs, may also be nested in one another in such amanner that the central valve plunger is held fully symmetricallythereby and any intrinsic stress in the springs may be completelydissipated by a minimal twist of the valve plunger. A soft suspension ofthe central valve plunger in the Z direction (i.e., perpendicular to thesurface extension of the first and second carrier layers) is implementedby the relatively great spring lengths, the spring height correspondingto nearly the entire functional layer height. In this state, the atleast one intake valve plunger and/or the at least one outlet valveplunger is still fixedly seated on the stop layer or sacrificial layersituated below the functional layer.

In particular in order to make the intake valve plunger adjustable inthe Z direction and/or to enlarge the pump chamber and/or the outletvalve chamber, in a refinement of the exemplary embodiments and/orexemplary methods of the present invention, the (upper) stop layer,which is used as a sacrificial layer, adjoining the functional layer isremoved in a way known per se, for example, with the aid of liquid orvaporized hydrofluoric acid. After this etching procedure, thefunctional unit “intake valve” is freely mobile and may thus bedeflected in the Z direction. The distance of the at least one coiledspring to the base layer may correspond to the thickness of thepreviously removed stop layer (sacrificial layer), which may beapproximately 4 μm to 5 μm. It is advantageous that as many areas aspossible of the described stop layer are also removed during thedescribed etching process, because they would later introduce undesiredcompression stress into the mechanical structure of the micropump.

The exemplary embodiments and/or exemplary methods of the presentinvention also results in a micropump, in particular for high-precisiondelivery of insulin, the micropump having multiple functional elements,such as at least one intake valve and at least one outlet valve and atleast one pump chamber. A micropump designed according to the concept ofthe exemplary embodiments and/or exemplary methods of the presentinvention is distinguished in that all functional elements of themicropump of this type are exclusively manufactured by structuringlayers from one direction. In other words, the functional elements arenot produced by two-sided structuring processes, but rather only bystructuring processes which are performed from one direction and fromone side. Fragile manufacturing states may thus be avoided and themicropump may be mass produced at high yield.

In a refinement of the exemplary embodiments and/or exemplary methods ofthe present invention, the micropump has a carrier layer, in particularmade of borosilicate glass, in which at least one fluid channel, inparticular an intake channel and/or an outlet channel, is/areintroduced. In addition, the carrier layer may directly delimit the pumpchamber.

A specific embodiment of the present invention in which the at leastone, which may be exclusively one, intake valve includes at least onecoiled spring, which is situated in such a way that it ensures a softsuspension of the valve plunger of the intake valve in the Z direction,is particularly advantageous. A specific embodiment having multiplenested coiled springs may be particularly used, in order to be able todissipate undesired material stress.

With respect to a use of the micropump as an insulin delivery pump forhigh-precision insulin metering, a specific embodiment may particularlybe used in which the intake valve of the micropump may be activelysealed using at least one actuator, which may be a piezoactuator, i.e.,a specific embodiment in which the intake valve of the micropump may bekept closed by appropriately triggering at least one actuator, in orderto thus prevent insulin entry into the micropump even for the case inwhich pressure is applied to the insulin supply itself. In other words,the delivery volume of the micropump becomes independent of the initialpressure in the insulin supply container, thereby achieving a highmetering accuracy. Above all, undesired drug flows or back flows of adelivered metering quantity are suppressed by the described specificembodiment and the metering dispensation is strictly linked to aso-called “stroke volume,” which is the quantity corresponding to onepump stroke.

In a specific embodiment a valve sealing surface of the intake valve,which is situated on a valve plunger in particular, may be pressedagainst the carrier layer using at least one actuator in order to thusavoid unintentional inflow of fluid, in particular insulin, into themicropump. A valve sealing surface of an outlet valve may also bepressed actively against the carrier layer using at least one actuator.

The mode of operation of an exemplary embodiment of a micropump isdescribed hereafter: which may be, the micropump, including a drugsupply (which may be an insulin supply) and optionally also an attachedinjection needle or a microneedle array may be installed, in particularclipped in, as a so-called “disposable article” in a device whichrepresents the so-called “pump” for the end-user. The “pump” may containthe control electronics, the power supply, for example by batteries orstorage cells, a user interface, and/or a wireless interface to a userinterface or to a telemedicine apparatus, or optionally also a wirelessinterface to a blood sugar value determination apparatus, whichtransmits measured blood sugar data to the “pump” for furtherprocessing. The “pump” may also contain the actuators of the micropump.These are up to three actuators, which may be three actuators, which acton positions provided for this purpose on the micropump, which may be onthe intake valve, on the pump diaphragm (i.e., on the pump chamber), andon the outlet valve. The up to three actuators may be configured in theform of so-called piezostacks, i.e., systems of piezoelectric discs orindividual elements connected in series in a cascade to form apiezoactuator in each case, which becomes shorter or longer through anapplied electrical voltage, depending on the polarity of the electricalvoltage in relation to the polarization of the piezoelements.

First, the pump function will be described using a system made of threeactuators, although it is possible to dispense with individual actuatorsand to relinquish the corresponding partial function or additionalsafety mechanism connected thereto.

After the installation of the micropump in the receptacle device(“pump”) provided for this purpose, the actuators are conditioned, i.e.,brought once into a defined position and fixed there:

-   -   so that a first actuator presses on a diaphragm (which may be        the base layer) below the intake valve plunger and the intake        valve is closed and blocked against the second carrier layer via        this diaphragm,    -   so that a second actuator just rests flatly on the diaphragm        (which may be the base layer) of the micropump and thus defines        its “starting position,” or alternatively simply presses the        diaphragm through up to the stop formed by the second carrier        layer;    -   so that a third actuator presses on the area of the outlet valve        plunger (in particular on the base layer) and closes and blocks        it against the second carrier layer.

The conditioning may be performed manually or which may be automatically(for example, motor-driven), in that, for example, an actuator block,including the three actuators positioned relative to one another, ismoved forward as a unit, until a resonant frequency change of one of theactuators (which may be the piezostack) indicates, for example, that acontact has occurred with the micropump, in particular the base layer,or a force is acting on the actuators. Because the actuator block isadvantageously moved forward as a unit and the individual actuators ofthe block were correctly positioned relative to one another beforehandby the manufacturer, the measurement on a single actuator, in particularon a single piezoelement, is sufficient in order to detect that theentire system has reached the correct location. For example, the contactof the actual pump diaphragm (which may be the base layer) with thesecond actuator is very easy to detect via its vibration behavior duringelectrical resonance excitation. The core idea of this conditioningmethod is that if only one actuator is advanced into its targetposition, the target positions of the other actuators are alsoautomatically correct, because they have been adjusted relative to oneanother on the actuator block. The method of simply bringing an actuatorto a hard stop is particularly simple, because it may be performedwithout measurement, i.e., for example, blocking the intake valve and/orthe outlet valve or pressing through the pump diaphragm up to the stop.For this purpose, the actuator block is advanced using defined forceuntil no further movement is possible because of the hard stop. Anactive measurement of the actuator position (for example, by resonantfrequency change) is superfluous in this case.

In a particular embodiment of the conditioning method, the conditioningis performed with the aid of at least one single spring or a springsystem, which simply presses the actuator block forward against themicropump without a further motor system. If at least one of the valves,either the intake valve or the outlet valve, is to be mechanicallyblocked, i.e., at least one of the two actuators acts unshortened on themicropump or its valve seats, the target position of the actuator blockrelative to the micropump is always defined. It is never provided inoperation of the pump that both the intake valve and also the outletvalve are both simultaneously unblocked, i.e., both associated actuatorswould be shortened. This functional feature allows particularly simplepositioning of the actuator block using a spring, which only must besufficiently strong to block the two valves reliably and press themagainst their stops—their valve seats. The position of the entireactuator block is thus also defined. The micropump is only inserted orclipped into the position provided for this purpose, for example, withina guide or in a lateral frame in the “pump,” the actuator block havingto be pushed back somewhat, which may be manually, for example, in orderto be able to receive the micropump. If the micropump has been broughtinto position, the springs of the actuator block are permitted to simplypress the latter against the micropump, whereby, for example, both theintake valve and also the outlet valve are blocked and simultaneouslythe actuator assigned to the pump diaphragm is also exactly defined inits position relative to the pump diaphragm.

In particular if a high dynamic response of the pumping action is to bedispensed with, it is possible to do without the pump diaphragm actuator(second actuator), for example, and replace it with a rigid spacerelement, for example, which presses on the pump diaphragm (which may bethe base layer). In this case, the two valve actuators may suffice toalso apply the pumping action themselves via the actuator block and thespacer element. For example, if the outlet valve is to be unblocked andsubsequently the pump diaphragm is to be brought into contact via“stroke,” the outlet valve actuator may be retracted by the thickness ofthe base layer of, for example, approximately 20 μm plus an additionaloffset of approximately 5 μm, which may be while exploiting thepiezoeffect. The intake valve actuator, for example, is subsequentlyretracted somewhat less than the base thickness layer, i.e., forexample, 19.5 μm, whereby the spacer element, which is central inparticular, advances with the actuator block by just this distance andpushes the pump diaphragm (which may be the base layer) against its stop(which may be the second carrier layer) or nearly against its stop. Inall described cases, it is very easily possible to bring the actuatorblock independently, through at least one simple spring or springsystem, into the desired position relative to the micropump, whichresults in ready handling during use of the micropump and also providesintrinsic safety: it is ensured by the passive spring action that in theelectrically deenergized state, all valves are blocked, i.e., “normallyclosed behavior” is provided. In this configuration, no insulin may passthrough the micropump, even if the supply container is placed underpressure, because both the intake valve and also the outlet valve arepressed closed by one actuator each.

The micropump operates as follows if three actuators are provided:

Before a pump stroke, the actuator directly assigned to the outlet valveis retracted by applying an electrical voltage to the piezostack, forexample, whereby the outlet valve is unblocked. This does not yet meanthat the outlet valve is opened; rather, it remains closed until it isopened by an overpressure in the interior of the micropump. Only thenmay insulin leave the micropump. Because the intake valve may still beblocked, no insulin may reach the micropump from the insulin supply.

The actuator directly assigned to the diaphragm of the micropump is nowlengthened, which may be done by applying an electrical voltage, andpresses the pump diaphragm (which may be the base layer) through up tothe upper stop, i.e., which may be up to the second carrier layer. Theso-called “stroke volume” is dispensed by the outlet valve.

As the next step, the outlet valve is blocked by lengthening theactuator assigned thereto (for example, by removing the electricalvoltage which had shortened the actuator or briefly reversing thepolarity of the voltage and only then setting it to zero) and thenshortening the first actuator assigned to the intake valve, for example,by applying an electrical voltage, whereby the intake valve isunblocked, but not yet opened. Rather, the intake valve remains closed,even against an overpressure from the outside in the insulin supply,because nothing may flow out of the micropump as a result of the blockedoutlet valve. The intake valve is opened and a “stroke volume” ofinsulin reaches the micropump only when the second actuator assigned tothe pump chamber is shortened, for example, by removing the electricalvoltage applied to the piezostack, and the pump diaphragm (which may bethe base layer) moves back into its starting position. The firstactuator assigned to the intake valve is then electrically deenergizedagain, whereby it stretches out up to its starting length and againblocks the intake valve. The pumping procedure may then be repeated. Thethird actuator (outlet valve actuator) unblocks the outlet valve, thesecond actuator (pump actuator) performs a “stroke,” and the “strokevolume” is delivered from the micropump through the outlet valve. Thethird actuator blocks the outlet valve and the first actuator unblocksthe intake valve, upon which the second actuator returns the pumpdiaphragm to its starting location, the previously dispensed “strokevolume” being replaced again from the insulin supply container via theintake valve and reaching the micropump, upon which the intake valve isblocked again using the first actuator, etc.

It is essential that only the “stroke volume” always reaches themicropump, independently of any possible initial pressure in the supplycontainer, and precisely this “stroke volume” is also always deliveredfrom the micropump, without a harmful backflow into the micropump. Themetering is thus very accurate and the micropump is intrinsically safe,even in the event of overpressure in the supply container. Because oftheir high longitudinal rigidity, piezoactuators suggest themselves asthe actuators, on the basis of which the function of the micropump wasdescribed as an example. However, it is also possible to use otheractuators, for example, thermal or electrical actuators, in particularhaving corresponding spring systems, as actuators, additionally oralternatively to piezoactuators.

Further advantages, features, and details of the present inventionresult from the following description of exemplary embodiments and onthe basis of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an initial method step for manufacturing a micropumpstarting from a silicon wafer as the first carrier layer.

FIG. 2 shows another initial method step for manufacturing a micropumpstarting from a silicon wafer as the first carrier layer.

FIG. 3 shows an alternative starting point for a manufacturing methodfor manufacturing a micropump, starting from an SOI wafer.

FIG. 4 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 5 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 6 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 7 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 8 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 9 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 10 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 11 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 12 shows important manufacturing step(s) for manufacturing amicropump, the first carrier layer being designed as a silicon wafer inthe method steps shown.

FIG. 13 shows essential method steps during the manufacturing of amicropump, the first carrier layer being part of the SOI wafer here, themethod step according to FIG. 13 corresponding to the method stepaccording to FIG. 9.

FIG. 14 shows essential method steps during the manufacturing of amicropump, the first carrier layer being part of the SOI wafer here, themethod step according to FIG. 14 corresponding to the method stepaccording to FIG. 11.

FIG. 15 shows essential method steps during the manufacturing of amicropump, the first carrier layer being part of the SOI wafer here, themethod step according to FIG. 15 corresponding to the method stepaccording to FIG. 12.

FIG. 16 shows a perspective view of a not yet finished micropump duringits manufacturing.

DETAILED DESCRIPTION

Identical components and components having identical functions areidentified using identical reference numerals in the figures.

In FIG. 1, the manufacturing of a micropump starts beginning with asilicon wafer as first carrier layer 1, which is provided on its frontside V with a (thermal) oxide as lower stop layer 2, in which contactholes 3 for an electrical contact between the base carrier layermaterial silicon and subsequently applied silicon layers are applied ata suitable location. The electrical contacts are advantageous for alater, so-called anodic bonding process, in which a current flow isrequired for the production of a high-strength bond to a second carrierlayer 4 (here: glass substrate), which is shown in FIG. 10, for example.

FIG. 2 shows a further intermediate stage of the micropump, a base layer5, which is designed as an epi-polysilicon layer, having been applied tothe front side of lower stop layer 2 during its manufacture. In thisexemplary embodiment, the thickness of base layer 5 is 11 μm. Base layer5 may optionally be planarized, for example, by a CMP step.

FIG. 3 shows an alternative starting point for the manufacturingprocess, which starts with a so-called SOI wafer 6 as the startingmaterial. The steps of films 1 and 2 may be dispensed with, because ahigher quality semifinished product is already used as the startingmaterial. However, it is disadvantageous in this case that there is noelectrically conductive connection available from lower, first carrierlayer 1 to upper base layer 5, which is situated on front side V offirst carrier layer 1, of SOI wafer 6 via contact holes. A suitablecontact arrangement must be provided via the wafer edge for later anodicbonding, such as clamps or spring contacts, which electrically contactupper base layer 5 of SOI wafer 6 from the edge, for example.

FIG. 4 shows the continuation of the manufacturing process,independently of whether the variant according to FIGS. 1 and 2 or thevariant according to FIG. 3 is followed. The variant according to FIGS.1 and 2 is illustrated hereafter on the basis of FIGS. 4 through 12,which begins from a silicon wafer as the starting point (first carrierlayer 1)—the “SOI wafer” variant may be readily derived therefrom.

A thick oxide is deposited on the front side of base layer 5 as upperstop layer 7 and structured in such a way that stop layer 7, which isused as the sacrificial layer, remains on selected surfaces. Theseselected surfaces are all areas in later manufacturing steps in which asilicon plasma etching process must be stopped and/or a freestandingmobile structure is to result. It is essential that a stop layer 7 isprovided directly above contact holes 3.

In the exemplary embodiment shown, the thickness of upper stop layer 7is approximately 4 μm to 5 μm. In the “SOI wafer” variant, for example,a thermal oxide up to a thickness of 2.5 μm is grown and an oxide whichis 1.8 μm thick is deposited over it, for example, in the form of TEOSor plasma oxide, which results in a total stop thickness layer of atmost approximately 4.3 μm. In the variant which begins with a siliconwafer as the first carrier layer, thermal oxidation is not recommended,because intolerable stress gradients would be introduced into the baselayer material (epi-polysilicon) in this manner, which would make thefurther use as a mechanical layer material impossible. For thelast-mentioned case, the deposition of the full stop layer thickness(oxide thickness) may be performed as TEOS or plasma oxide at relativelylow temperatures of 300° C. to 450° C., for example.

In FIG. 5, a manufacturing step is shown in which a functional layer 8having a thickness of approximately 15 μm to 24 μm was deposited on thefront side of base layer 5 and on the front side of stop layer 7.Functional layer 8 is made of an epi-polysilicon layer in the exemplaryembodiment shown. Because anodic bonding must be performed later on thefront side (layer surface) of functional layer 8, planarization of thesurface, for example, by a CMP method, is to be unconditionallyrecommended here, independently of whether base layer 5 was alreadyplanarized beforehand or an SOI wafer layer was used for the base layer.The planarization step must level out the topography of the surface andmicroscopically “smoothe” the surfaces for bonding.

In FIG. 6, the wafer stack is shown after the application andstructuring of an anti-bond layer 9, which must remain on the latervalve sealing surfaces. Anti-bond layer 9 may be made of siliconnitride, silicon carbide, or graphite, for example. In addition,recesses 10, 11 have been etched around anti-bond layer surface areas 9at a depth of approximately 2 μm to 5 μm. These recesses 10, 11 are notto come into contact with second carrier layer 4 to be bonded later, inorder to guarantee a mobility of microfluidic functional elements to bemanufactured, an intake valve plunger 14 and an outlet valve plunger 17here.

In FIG. 7, functional layer 8 has been structured, inter alfa, in thearea below recesses 10, 11. In other words, microfluidic functionalelements 12 are provided thereby, namely an intake valve 13 having anintake valve plunger 14, on whose front side anti-bond layer 9 islocated as the valve sealing surface. Furthermore, a pump chamber 15 andan outlet valve 16 having an outlet valve plunger 17 are provided, ananti-bond layer 9 also being located as the sealing surface on the frontside of outlet valve plunger 16. Functional elements 12 are not yetfinished in the method step according to FIG. 7. For this purpose, it isstill necessary, as shown in FIG. 8, to selectively remove upper stoplayer 7 (sacrificial layer). This may be performed in a way known per seby liquid or vaporized hydrofluoric acid. After this etching, intakevalve 13 or intake valve plunger 14 is freely mobile and mayparticularly be deflected in the Z direction. The distance of intakevalve plunger 14 to base layer 5 corresponds to the thickness of thepreviously removed oxide (upper stop layer 7 (sacrificial layer)) of 4μm to 5 μm.

The implementation of intake valve 13 is noteworthy here. In theexemplary embodiment according to FIG. 7, it includes a coiled spring18, which is shown in a top view below the wafer stack in FIG. 7. Coiledspring 18 carries intake valve plunger 14 on its end, whereby a softmounting of intake valve plunger 14 in the Z direction is provided andmaterial stress may relax.

An alternative specific embodiment of intake valve 14 results from theperspective view according to FIG. 16. Three nested coil springs 18 areshown, which are all connected at one end to intake valve plunger 14 atuniformly distributed positions around the circumference. Central intakevalve plunger 14 is held completely symmetrically by coiled springs 18and any intrinsic stress of the coiled springs is completely dissipatedby a minimal twist of intake valve plunger 14. A soft suspension of thecentral intake valve plunger in the Z direction is implemented by therelatively great spring lengths, the spring height corresponding tonearly the entire sacrificial layer height. Furthermore, the structureand the configuration of outlet valve 16 having its central valveplunger 17 is shown in FIG. 16. It may be seen from FIG. 16 that both anintake valve chamber and also an outlet valve chamber and pump chamber15 are contoured as circular and are connected to one another via largeopening cross sections.

As previously noted, an intermediate step of the manufacturing of themicropump is shown in FIG. 8, in which (upper) stop layer 7 (sacrificiallayer) was selectively removed. Intake valve 13 is first unblocked inthis manner. Previously, intake valve plunger 14 still sat fixedly onthe thick oxide which forms stop layer 7 (sacrificial layer), and whichhas also formed the etch stop for the plasma etching process forstructuring functional layer 8.

It is clear from FIGS. 6 through 8 in particular that the manufacturingof functional elements 12 is exclusively performed by front sidestructuring, i.e., by structuring in a direction toward front side V ofthe first carrier layer. Carrier layer 1 was not involved here, becauseit has been structured through.

FIG. 9 illustrates an anodic bonding process: Pre-structured secondcarrier layer 4, a borosilicate glass wafer here (such as a Pyrex glasswafer), has holes at appropriate positions as fluid channels 19, 20.Left fluid channel 19 in the drawing forms an intake channel forsupplying drug (insulin) and fluid channel 20, which is on the right inthe plane of the drawing, forms an outlet channel for letting out a“stroke” volume. Fluid channel 19 may be connected to a storage tank orstorage bag having insulin and fluid channel 20 is attached to aninjection needle or particularly to a microneedle array, for example,made of porous silicon, etc. The peripheral edges of the lower ends offluid channels 19, 20 form the valve seats for intake valve plunger 14and outlet valve plunger 17. The anti-bond layer surface sections formthe sealing surfaces of intake valve 13 and outlet valve 16.Additionally or alternatively to anti-bond layer 9, anti-bond surfaces(not shown) may be provided as seat surfaces on the rear side of secondcarrier layer 4.

For the anodic bonding process, functional layer 8 must be contactedusing an electrical voltage source and positively polarized in relationto second carrier layer 4, which is applied with calibration. In thevariant shown, starting from a silicon wafer as first carrier layer 1,this contacting is readily possible via first carrier layer 1 because ofcontact holes 3 in lower stop layer 2. Voltages from a few hundred voltsto a few thousand volts are used in a way known per se, depending on thethickness of second carrier layer 4. A high-strength, high-precision,and irreversible bonding of the contact surfaces to one another isachieved by the anodic polarity of the front side or the silicon surfaceof sacrificial layer 8 in relation to second carrier layer 4, without anadhesive being required for this purpose. The latter is decisive inconnection with the restricted stability and bioactivity of insulin,which would be impaired in its effectiveness by many materials, such asmany plastics or adhesives. In the micropump shown, the insulin onlycomes into contact with silicon, borosilicate glass, and the anti-bondlayer inside the micropump—all of these materials have good insulincompatibility.

FIG. 10 shows the bonded wafer structure after the performance of theanodic bonding process.

In FIG. 11, first carrier layer 1 has been removed. The back thinning offirst carrier layer 1 may be performed by back grinding, plasma etching,or a combination of back grinding and plasma etching. Alternatively, wetetching may also be performed, for example, in hot potassium hydroxidesolution employing an etching mask as the front side protection. Theremoval of complete first carrier layer 1 by plasma etching isparticularly gentle, because no mechanical action occurs here. Becauseanisotropic etching is not required for this purpose per se, forexample, an isotropic SF₆ process having advantageous higher ablationrates of 50 to 100 μm/minute or more may be used for etching, forexample, so that the removal of first carrier layer 1 only takes a fewminutes. Because an etching attack on base layer (silicon here) lyingabove it up to (second) stop layer 7 occurs via contact holes 3, it isadvantageous to change over from purely isotropic plasma etching to atleast partially anisotropic plasma etching in the final phase of theprocess. The advantage of anisotropy is in the case in which contactholes 3 may be overetched, for example, to compensate for etchinginhomogeneities or wafer thickness variations over the wafer surface,without the etching into the base layer in the contact hole areasbecoming ever larger laterally. The disadvantage is the lower etchingspeed during anisotropic etching. The changeover from a purely isotropicetching process to an at least partially anisotropic plasma etchingprocess may be implemented in that, according to the teaching of DE 42410 45 A1, the isotropic SF₆ etching step is alternately performedtoward the end of the back etching with so-called passivation stepsusing C₄F₈ or C₃F₆ as the passivation gas, for example. The detection ofthis transition may be performed using an optical endpoint detection via“optical emission spectroscopy”—so-called OES—in that the reaching oflower (first) stop layer 2 at any location is detected and thepassivation steps are incorporated for the further etching or furtheroveretching, so as not to excessively laterally expand contact holes 3,which have already been attacked in the etching, during the overetching.The thick oxide layer which is opposite to contact hole 3 isetch-limiting in the vertical direction in each case. Using thisprocedure, inhomogeneities of the etching process itself or waferthickness variations may be compensated for by overetching withoutpenalty. The OES endpoint detection system indicates whether the firstcarrier layer, i.e., all of the silicon, was removed from lower stoplayer 2 and the process has reached its end.

FIG. 12 shows the removal of still remaining stop layers 2, 7: on theone hand, flat lower stop layer 2, on the other hand, upper stop layer 7(sacrificial layer) (etch stop area above open contact holes 3). Theremoval may again be performed by liquid or vaporized hydrofluoric acid.Because oxide layers in particular introduce strong compression stressesinto the mechanical structure, it is advantageous to remove all oxidelayers at the process end.

Furthermore, a possible system of a first actuator A1, a second actuatorA2, and a third actuator A3 is shown in FIG. 12. First actuator A1 isassigned directly to intake valve 13, second actuator A2 is assigneddirectly to pump chamber 15, and third actuator A3 is assigned directlyto outlet valve 16. It may be seen that all actuators A1 through A3 actdirectly on base layer 5, which delimits the micropump on the sidefacing away from second carrier layer 4. Reference is made to thegeneral part of the description with respect to the mode of operationand a possible triggering of actuators A1 through A3. In particular, itis to be noted that if needed, for example, second actuator A2 may bedispensed with (compare general part of the description).

FIG. 13 illustrates the bonding process for the case of the “SOI wafer”variant. Except for the difficulty of electrically contacting the upperSOI layer (base layer 5) via contact springs, etc., from the side or viathe wafer edge, because there are no contact holes to lower, firstcarrier layer 1, the structure and the procedure correspond precisely tothe counterpart of FIG. 9.

FIG. 14 shows the bonded wafer stack after the removal of first carrierlayer 1. Because there are no contact holes in lower stop layer 2 in theSOI structure, the removal of first carrier layer 1 is possibleparticularly readily and easily by backetching in plasma. It isadvantageous to monitor the isotropic silicon etching via SF₆ plasmausing an endpoint detection system (OES). This indicates when silicon isno longer etched and when lower stop layer 2 has been reached overall,lower stop layer 2 representing the etch stop for this etching process.Overetching may also be provided for security, in order to actuallyremove all silicon from lower stop layer 2 without residue andcompensate for any inhomogeneities. Because the entire process may beperformed isotropically, ablation rates are extremely high (typically100 μm/minute or more) and the processing time is very short (only a fewminutes). Alternatively, wet etching may also be performed, for example,in hot potassium hydroxide solution employing an etching mask as thefront side protection.

FIG. 15 shows the state of the wafer stack after the removal of lowerstop layer 2 by liquid or vaporized hydrofluoric acid. Removing alloxide also suggests itself in this case, in order to remove undesiredcompression stresses from the mechanical structure. The function ofactuators A1 through A3 shown is explained in the general part of thedescription.

In summary, a manufacturing process is proposed in the figures, which isexclusively based on standard processing steps of microsystem technologyor semiconductor technology in both variants shown (silicon wafer/SOIwafer). Fragile wafer states or wafer intermediate states do not occurat any point in time of the process, in which the wafer or the waferstructure must be stabilized by films or similar complex specialmeasures. Rather, robust structures are dealt with in all processstages, which may be handled and processed without special measures. Allchannels through which liquids are to flow during operation of themicropump have comparatively great channel heights of 15 μm to 24 μm,for example, and low flow resistances and small “dead volumes” as aresult thereof. This is all implemented using a comparatively simple andparticularly cost-effective process.

1-23. (canceled)
 24. A method for manufacturing a micropump, the methodcomprising: providing multiple layers on a front side of a first carrierlayer, which has a front side and a rear side; and forming microfluidicfunctional elements by structuring at least one of the layers, whereinthe structuring of the at least one layer for manufacturing allmicrofluidic functional elements is exclusively performed by front sidestructuring.
 25. The method of claim 24, wherein a second carrier layeris situated at a distance to the first carrier layer.
 26. The method ofclaim 25, wherein the second carrier layer has at least one fluidchannel before or after it is installed.
 27. The method of claim 26,wherein the first carrier layer is removed after the second carrierlayer is installed, by at least one of isotropic etching, back grinding,and wet etching.
 28. The method of claim 24, wherein the first carrierlayer remains unstructured during the front side structuring.
 29. Themethod of claim 24, wherein a silicon layer, which is a silicon wafer,is used as the first carrier layer.
 30. The method of claim 24, whereina stop layer, which contains silicon oxide, which is a thermal oxidelayer, is situated directly on the front side of the first carrierlayer, or the carrier layer is a component of an SOI wafer structurehaving an integral stop layer.
 31. The method of claim 30, wherein thestop layer is provided with at least one contact hole for producingelectrical connections between the first carrier layer and layerssituated on the front side of the first carrier layer.
 32. The method ofclaim 30, wherein a base layer, containing silicon, is situated directlyon the front side of the stop layer, or the base layer is an integralcomponent of the SOT wafer.
 33. The method of claim 32, wherein a stoplayer, which contains a silicon oxide, and is configured as asacrificial layer, is situated and structured directly on the front sideof the base layer.
 34. The method of claim 33, wherein a functionallayer, which is formed as an epi-polysilicon layer, is situated on thefront side of the stop layer situated on the base layer and on the frontside of the base layer.
 35. The method of claim 34, wherein at least onedepression is introduced into the functional layer in an area which isnot to come into contact with the second carrier layer.
 36. The methodof claim 34, wherein at least one anti-bond layer is situated on thefront side of the functional layer as at least one of a valve sealingsurface and at least one anti-bond layer is situated on the rear side ofthe second carrier layer as a valve seat surface.
 37. The method ofclaim 34, wherein at least one of an intake valve structure, a pumpchamber structure, and an outlet valve structure is introduced bystructuring the functional layer.
 38. The method of claim 37, wherein atleast one of the intake valve structure and the outlet valve structureare produced having at least one coiled spring section.
 39. The methodof claim 37, wherein the stop layer, which is configured as asacrificial layer, is removed at least partially on the front side ofthe base layer, using at least one of liquid hydrofluoric acid andvaporized hydrofluoric acid.
 40. A micropump, comprising: multiplelayers on a front side of a first carrier layer, which has a front sideand a rear side; and microfluidic functional elements, which are formedby structuring at least one of the layers, wherein the structuring ofthe at least one layer for manufacturing all microfluidic functionalelements is exclusively performed by structuring from one direction. 41.The micropump of claim 40, wherein the micropump has a carrier layer,which is a borosilicate glass layer, into which at least one fluidchannel, which includes at least one of an intake channel and an outletchannel, is introduced.
 42. The micropump of claim 40, wherein theintake valve of the micropump has at least one coiled spring carrying avalve plunger.
 43. The micropump of claim 40, wherein at least one ofthe intake valve and the outlet valve of the micropump can be activelysealed using at least one actuator.
 44. The micropump of claim 43,wherein at least one of a valve sealing surface of the intake valve anda valve sealing surface of the outlet valve can be pressed against thecarrier layer using an actuator.
 45. The micropump of claim 40, whereinat least one actuator is directly assigned to each of the intake valve,the outlet valve, and the pump chamber.
 46. The micropump of claim 40,wherein at least one actuator is directly assigned to only the intakevalve and the outlet valve, and the pumping action is controllable bytriggering at least one of these actuators.
 47. The micropump of claim40, wherein the micropump is for providing a metered delivery ofinsulin.
 48. The micropump of claim 40, wherein the micropump has acarrier layer, which is a borosilicate glass layer, into which at leastone fluid channel, which includes at least one of an intake channel andan outlet channel, is introduced, and which directly delimits the pumpchamber.
 49. The micropump of claim 40, wherein the intake valve of themicropump has at least one coiled spring carrying a valve plunger,having multiple nested coiled springs.
 50. The micropump of claim 40,wherein at least one actuator, which is a piezoactuator, is directlyassigned to each of the intake valve, the outlet valve, and the pumpchamber.
 51. The method of claim 24, wherein a second carrier layer,which is a borosilicate glass wafer, is situated, by being anodicallybonded, at a distance to the first carrier layer, and on the front sideof the layer furthest away from the first carrier layer.
 52. The methodof claim 51, wherein the second carrier layer has at least one fluidchannel, with an inflow channel and an outflow channel, before or afterit is installed.
 53. The method of claim 34, wherein at least onedepression is introduced into the functional layer in an area which isnot to come into contact with the second carrier layer, which is to besituated on the front side of the functional layer.
 54. The method ofclaim 34, wherein at least one of an intake valve structure, a pumpchamber structure, and an outlet valve structure is introduced bystructuring the functional layer, by trench etching.
 55. The method ofclaim 37, wherein at least one of the intake valve structure and theoutlet valve structure are produced having at least one coiled springsection, having multiple nested coiled spring sections.
 56. The methodof claim 24, wherein the micropump is for providing a metered deliveryof insulin.